1. Field of the Disclosure
Embodiments disclosed herein relate generally to well control devices used in oil and gas exploration. In particular, embodiments disclosed herein relate to packing units capable of sealing varying tubular diameters in a wellbore.
2. Background Art
Referring initially to FIG. 1, a prior art annular blowout preventer 101 is shown. Annular blowout preventer 101 includes a housing 102 having a central bore 120 extending therethrough along a borehole axis 103. A packing unit 105 is disposed within annular blowout preventer 101 about central bore 120, such that a bore 111 of the packing unit 105 is substantially concentric with bore 120 of blowout preventer 101.
As depicted in FIG. 1, packing unit 105 includes an elastomeric annular body 107 and a plurality of metal inserts 109. Metal inserts 109 are shown disposed within elastomeric annular body 107 of packing unit 105 in radial planes in a generally circular fashion about borehole axis 103. In use, hydraulic fluid may enter a cylinder 112 through an activation port 113, thereby thrusting an actuation piston 117 in an upward direction. As piston 117 is thrust upward, an inclined surface 118 of actuation piston 117 compresses packing unit 105 so that bore 111 is reduced as metal inserts 109 are displaced toward borehole axis 103. To open bore 111, hydraulic fluid is diverted to a retraction port 115 and piston 117 is urged in a downward direction.
Thus, conventional packing units (e.g., 105) generally include large toroid-shaped elastomeric (or rubber) seal devices that may not be able to withstand the elevated temperatures and pressures encountered in various drilling situations. As wells are drilled deeper into the earth and in deeper waters offshore, the temperatures and pressures of returning drilling fluids are increasing to levels exceeding those previously experienced. As a result, elastomers that were flexible enough to be used in former packing units may soften too severely under the higher temperatures and therefore may lose their ability resist failure by extrusion through the large “gap” in the annular space between inclined surface 118 and bore 120.
Additionally, metal inserts 109, historically disposed within the elastomeric body 107 to strengthen the packing unit 105, may not be able to provide sufficient structural support to prevent the elastomeric body 107 from failing at the elevated temperatures and pressures experienced in such deep well drilling environments. While elastomers capable of exhibiting suitable high-temperature resistance may be available, such elastomers are too stiff at lower temperatures to be usable in packing units. When used at lower temperatures, the stiffer, high-temperature, elastomers may not be able to sufficiently deform to seal about a tubular or other object contained within bore 120.
Therefore, for annular packing units to function properly (i.e., form stable seals between the bore 120 and an object contained within the bore 120) in wells having high temperature and pressure, packing units must maintain an appropriate amount of flexibility yet retain sufficient strength across the entire anticipated operating range of temperatures and pressures. In certain high-temperature applications, absent the development of new elastomer compounds, interchangeable (or multiple) packer elements, each having a elastomer combination tailored for a particular sub-set of the overall temperature and pressure range, would be necessary. However, as many high-temperature and high-pressure drilling applications occur at deep sea depths, the ability to deploy a system using interchangeable packer elements is limited.
Therefore, an improved mechanism for a packing unit of an annular and/or a ram-type blowout preventer would be highly desirable. For example, if an annular blowout preventer were constructed with a packing element capable of accommodating a range of sizes without experiencing significant strains, the pressure and temperature ratings of the annular blowout preventer may be increased and one or more ram-type blowout preventers removed from the BOP stack.
Accordingly, there exists a need for a robust packing element capable of withstanding elevated temperatures and pressures, while simultaneously providing adequate sealing capabilities about a variety of objects of varying size.